Conventionally, a power conversion device, such as an inverter and a converter, may use a diode built-in transistor that has a transistor and a diode provided on the same substrate.
The diode built-in transistor has an electrode common to the collector electrode of the transistor and the cathode electrode of the diode, and an electrode common to the emitter electrode of the transistor and the anode electrode of the diode. Therefore, when a gate signal is input into the transistor to turn on the transistor, the anode and the cathode of the diode tend to take the same potential, which makes it difficult for the diode to operate in the forward direction. Consequently, gate interference may occur that increases the forward voltage of the diode. Thus, in a case where the diode conducts electricity, if a gate signal is input into the transistor to turn on the transistor, there is a problem that the forward-directional loss of the diode increases.
Thereupon, a technology has been proposed that determines whether the diode conducts electricity in a diode built-in transistor, and if the diode conducts electricity, inhibits the gate signal from being input into the transistor (for example, Patent Document 1). Specifically, the technology has the diode and the transistor provided with sense elements for current detection, and determines whether the diode conducts electricity, based on the direction of a current flowing in a sense resistor connected with the sense elements, namely, whether the voltage between both terminals of the sense resistor takes a positive value or a negative value. This prevents the transistor from turning on when the diode conducts electricity, and hence, it is possible to prevent the forward-directional loss of the diode from increasing.